The paramyxovirus group of animal viruses includes human pathogens responsible for respiratory and neurologic disorders as well as the causative agents of economically significant diseases of domestic livestock. Despite their importance as agents of infectious disease, we have only meager knowledge about the molecular interactions which transpire between viral macromolecules and cellular components during infection. We plan to use transmission electron microscopy and cellular fractionation techniques to monitor intracellular events during the infection of cultivated chicken embryo cells by temperature-sensitive and noncytopathic mutants of a virulent strain of Newcastle disease virus. The objective of the proposed study is to identify and characterize mutants with defects in viral morphogenesis and which exhibit altered intracellular distributions of viral components. Characterization of mutants possessing such defects will contribute to the elucidation of the normal pathways of virion assembly and to an understanding of the interactions between viral macromolecules and cellular components which potentiate cellular destruction. In addition, we plan several studies designed to increase our basic knowledge of the genome strategy of paramyxoviruses. These experiments include: (a) correlation of the mRNA of NDV with the protein for which each codes, (b) analysis of the putative precursor of the nucleocapsid protein and its mode of processing, (c) investigation of the mechanism of enhancement of cellular protein synthesis by amino acid analogues and its relation to paramyxovirus-mediated stimulation of cellular protein accumulation.